The present invention relates to a method for controlling a continuously variable transmission installed in a vehicle, and more particularly to a method for controlling a rate e of changing a RPM ratio between a driving pulley and a driven pulley in a continuously variable transmission.
A major factor influencing the use of a continuously variable transmission in a vehicle is to decrease the amount of fuel consumed by the engine. The continuously variable transmission continuously varies a transmission RPM ratio "e" between a driving pulley and a driven pulley, i.e. [e=(a rotating speed of an output shaft)/(a rotating speed of an input shaft), RPM.sub.out /RPM.sub.in ]. The transmission efficiency of a continuously variable transmission can be represented as a linearly declining function of the rate of changing the RPM ratio e, represented by e. The rate e of changing the RPM ratio is always referred to as a positive quantity, for example, the absolute value of the rate of change is referred to as .vertline.e.vertline. or .vertline.de/dt.vertline..
Previous attempts to control the rate e of changing the transmission RPM ratio have involved utilizing a fixed rate ef of changing the transmission ratio, which was completely independent of the amount that a throttle valve was opened (.theta.) or the rate that the throttle valve was opening or closing, i.e. .vertline.d.theta./dt.vertline.. Therefore, if the rate e of changing the transmission RPM ratio was fixed at a high value, whenever rapid acceleration of the vehicle was required, the transmission could rapidly respond. However, a large amount of fuel was consumed whenever the vehicle was exposed to steady state driving conditions or when required to slowly accelerate. Conversely, if the rate e of changing the transmission RPM ratio was fixed at a small value, only a small amount of fuel was consumed whenever the vehicle was exposed to steady state driving conditions or when slowly accelerating. However, the transmission could not rapidly respond when a rapid acceleration of the vehicle was required.